The proposed investigation is designed to determine whether or not the two most frequently used positive contrast media for human ventriculography induce cellular damage in the brain of the rhesus monkey. The contrast media, Pantopaque and Conray, will be injected intraventricularly into several experimental groups of juvenile and adult monkeys including (1) normal animals, (2) animals in which hydrocephalus has been induced by blocking the fourth ventricle with a balloon, and (3) monkeys that have received silicone injections into the cisterna magna to impede but not completely block the exit of the ventricular cerebrospinal fluid. X-ray skull films will be taken periodically in order to ascertain the relative amount, if any, and location of retained contrast media. This information will later be correlated with the histologic examination after necropsy. The animals will be sacrificed at various time intervals, varying from 5 minutes to 1 year, following the ventricular injections. Specific regions of the choroid plexus, ventricular wall, and subarachnoid space will be studied with both light and electron microscopic techniques. A detailed description of both the normal appearance and any deviation from this induced by the contrast media will be presented. The findings of the study of the tissue from the adult animals will be compared with those from the juvenile monkeys to determine whether there is a difference in normal structure or in the reaction to the contrast media between the two age groups. A concerted effort will be devoted to perfecting a ferritin-conjugated antibody technique for tracing the uptake and transport of the contrast media at the ultrastructural level.